1. Field of the Invention
The present invention relates to a novel catalyst composition and its use in cracking hydrocarbons. The catalyst is particularly useful in producing light olefins, preferably from paraffins. When used to convert paraffins to light olefins, the catalyst is capable of high paraffin conversion, high olefin yield, and low aromatic yield.
2. Discussion of Background Information
Current technologies for the production of light olefins, e.g. ethylene, propylene and, optionally, butylenes can be classified into the two categories of thermal cracking (also known as steam cracking) and catalytic cracking. While these technologies have been practiced for many years and are considered the workhorses for light-olefin production, both have disadvantages.
Steam or thermal cracking, a robust technology that does not utilize catalyst, produces the more valuable ethylene as the primary light olefin product. It is particularly suitable for cracking paraffinic feedstocks to light olefins. However, steam cracking is an expensive, complex technology due to required special construction material to sustain high cracking temperatures (˜1600° F.) and high energy input. Sulfur addition is required to passivate the furnace metal surfaces on a continuous basis, creating such undesirable side effects as environmental and product contamination. Steam cracking is not considered to be suitable for cracking feeds containing high concentrations of light olefins as it makes high levels of low value heavy by-products due to the more reactive nature of the olefin feeds. In addition, steam cracking makes a relatively low amount of propylene, and, therefore, is not considered suitable for meeting the anticipated growing demand for propylene in the future. Also, steam cracking requires steam dilution to control product selectivity and to maintain an acceptable run length; steam dilution is costly in terms of capital investment and energy consumption.
Current catalytic cracking technologies employ solid acid catalysts such as zeolites to promote cracking reactions. Unlike steam cracking technology, propylene is the primary light olefin product of catalytic cracking. Accordingly, catalytic cracking would he considered as the main source for growing propylene demand. Catalytic cracking (cat cracking) is typically operated at lower temperatures than steam cracking. Also, special treatments such as sulfur injection and special construction materials are not necessary. However, cat cracking also has its drawbacks. Currently, cat cracking mostly operates at less than 1100° F. and can only convert the more expensive and relatively rare olefinic feeds to light olefins. It is not capable of cracking the more cost-effective and more abundant paraffinic feeds to acceptable yields. Paraffins are less reactive than olefins. To achieve significant paraffin conversion, cracking paraffins requires more active catalyst which operates at temperatures greater than 1200° F., which, in turn, requires catalyst regeneration at above 1300° F. To this point in time, there have been no commercially satisfactory catalysts at such severe conditions. Also, by material balance, acid cracking of a paraffin molecule generates a smaller olefin molecule and a smaller paraffin molecule. This is relatively undesirable compared to cracking an olefin molecule, which usually generates two smaller olefin molecules. Consequently, the yield of light olefins from cat cracking of paraffin feeds becomes significantly lower than that from cracking olefins. Furthermore, selectivity to light olefins decreases with increasing temperature. In addition to light paraffins, other by-products such as the relatively lower valued aromatic compounds become significant at temperatures greater than 1200° F. It is also significant that cracking paraffins to light olefins is highly endothermic. How to provide the large amount of heat input into a commercial catalytic reactor at temperatures greater than 1200° F. is an engineering challenge.
U.S. Pat. No. 4,497,971, which is incorporated herein by reference in its entirety, relates to an improved catalytic process for the cracking and oxidative dehydrogenation of light paraffins, and a catalyst therefor. According to this patent, a paraffin or mixtures of paraffins having from 2 to 5 carbon atoms is oxidatively dehydrogenated in the presence of a cobalt-based catalyst composition which not only has oxidative dehydrogenation capabilities but also has the capability to crack paraffins having more than two carbon atoms so that a paraffin such as propane can be converted to ethylene. If the feed to the oxidative dehydrogenation process contains paraffins having more than two carbon atoms, some cracking of such paraffins will occur at the conditions at which the oxidative dehydrogenation process is carried out.
U.S. Pat. No. 4,781,816, which is incorporated herein by reference in its entirety, relates to a catalytic cracking process and to a process for cracking heavy oils. It is an object of the disclosed invention to provide a process for cracking hydrocarbon containing feedstocks, which contain vanadium compounds as impurities. According to this patent, the feedstream to be treated contains at least about 5 wppm vanadium. The catalyst comprises a physical mixture of zeolite embedded in an inorganic refractory matrix material, and at least one oxide of a metal selected from the group consisting of Be, Mg, Ca, Sr, Ba and La (preferably MgO) on a support material comprising silica.
U.S. Pat. No. 5,002,653, which is incorporated herein by reference in its entirety, relates to an improved catalytic cracking process using a catalyst composition for use in the conversion of hydrocarbons to lower-boiling fractions. More particularly, the invention comprises a process for using a dual component catalyst system for fluid catalytic cracking, which catalyst demonstrates vanadium passivation and improved sulfur tolerance. The catalyst comprises a first component comprising a cracking catalyst having high activity, and, a second component, as a separate and distinct entity, the second component comprising a calcium/magnesium-containing material in combination with a magnesium-containing material, wherein the calcium/magnesium-containing compound is active for metals trapping, especially vanadium trapping.
A significant need exists for a cracking technology which overcomes the above-discussed disadvantages of present, commercial cracking technology. It is believed that no catalytic cracking of paraffins is performed commercially at this time.